This invention relates to composite materials formed by thermoplastic materials reinforced by fibers. More particularly, this invention relates to such composite materials, and to methods and apparatus for forming such materials, where the thermoplastic and fiber components are such as to impart to the composite materials enhanced strength as compared with materials made previously to this invention.
The forming of composite materials using polymers and fibers has been known heretofore, and apparatus, processes and products relating to such composite materials are disclosed in, for example, Singer U. S. Pat. No. 4,341,822; Hawley U.S. Pat. No. 4,439,387; Cogswell U.S. Pat. No. 4,549,920; and Cogswell U.S. Pat. No. 4,559,262, to which the interested reader is referred for reviews of still earlier prior disclosures. At least certain of the mentioned disclosures describe composite materials formed using thermoplastic polymers and structural reinforcement fibers such as glass, aramids, metallic fibers or the like, and address the difficulties of obtaining penetration of polymers into the fibers and embedment of the fibers within a body of the polymeric material. The relative penetration or embedment, or ease of accomplishing such penetration or embedment, has been referred to heretofore (and will be here referred to) as the "wetting" of the fiber with the polymeric material.
Composite materials of the broad class identified above have been formed using both thermosetting and thermoplastic polymeric materials. The difficulties of producing composite materials with the two classes of polymeric materials differ substantially, due to the characteristics of the polymeric materials. The present invention is concerned only with thermoplastic materials, as to which wetting has been a previously insurmountable problem with high melt viscosity thermoplastic materials. This has been a limiting factor of the strength attainable by such materials, as stronger thermoplastics typically also have higher viscosities.